Suspensions for vehicles such as trucks and the like are very well known in the art.
Indeed, a conventional vehicle suspension connects an axle to the structural frame, or chassis, and includes a combination of springs and shock absorbers for absorbing, isolating and dampening the movements transmitted between the axle and the chassis. Typically, a vehicle such as a truck will include a front axle supporting a pair of front wheels and at least one rear axle supporting a pair of rear wheels. A second (rear tandem) and even third (rear tridem) rear axle can be provided to increase the load capacity of a given truck.
It is also known in the art to provide a second front axle to further increase the load capacity of a truck. Such a front suspension is called a front tandem suspension.
Canadian Patent No. 2,070,859, issued Jan. 10, 1995 to Simard and titled “Tandem Axle Suspension for Vehicle”, describes a front suspension for a truck or semi-trailer including front and rear tandem axles connected to a vehicle chassis by first and second leaf springs, respectively. In order to distribute the load evenly between the front and rear axles, an equalizer beam is provided rockably mounted onto the chassis and connected at one end to the rear extremity of the first leaf spring, and at the other end to the front extremity of the second leaf spring.
U.S. Pat. No. 6,382,659, issued May 7, 2002 to Simard and titled “Load Distributing Tandem Suspension Assembly”, describes a front tandem suspension similar to that described above, with the addition of an air spring and a shock absorber for supporting the second front axle in conjunction with the second leaf spring.
Also known in the art, are the following patents and published patent applications: U.S. Pat. No. 3,460,851, U.S. Pat. No. 3,833,236, U.S. Pat. No. 3,871,677, U.S. Pat. No. 3,202,440, U.S. Pat. No. 4,420,171, U.S. Pat. No. 5,820,149, U.S. Pat. No. 7,195,272 and WO 2007/035648.
Tandem suspension systems typically include a pivot assembly which links an extremity of each leaf spring to vehicle's chassis. In order to improve driver comfort and minimize wear on the vehicle, it is known to provide an elastomeric element, such as a sleeve or bushing at a pivot point between a leaf spring and the chassis. This bushing is operable to absorb the micro-shocks and oscillations imparted from the road during operation.
It is known to mechanically link the front and rear leaf springs in a tandem suspension in order to share load therebetween. Due to the variety of arrangements that such suspension systems may utilize to connect, and distribute load between, the front and rear leaf springs, there exist a number of possible placements for such an elastomeric bushing between suspension elements.
For example, the tandem suspension disclosed in U.S. Pat. No. 6,382,659 (Simard) provides an equalizer beam extending between the front and rear extremities of the rear and front leaf springs. The equalizer beam is pivotally mounted to the chassis by a bracket and operable to distribute suspension loads between the leaf springs. It is known to provide the elastomeric element at the pivoting connection of the equalizer beam and its bracket.
For example, U.S. Pat. No. 3,279,815, issued Oct. 18, 1966 to Hutchens and titled “Suspension Assembly for a Vehicle and Process”, describes a first resilient sleeve which is fixed between an axle and a torque arm and second resilient sleeve which is fixed between the chassis and a balancer.
Similarly, U.S. Pat. No. 3,186,731, issued Jun. 1, 1965 to Fossard and titled “Vehicle Suspensions”, describes a rubber sleeve fixed between the equalizer and the pivotal support therefor.
For its part, U.S. Pat. No. 2,653,035, issued Sep. 22, 1953 to Ward and titled “Torque Rod Assembly for Spring Suspension”, describes a rubber bushing fixed between an axle and a torque arm.
Also known in the art are the various disadvantages associated with these types of conventional suspension systems.
The elastomeric bushings in conventional suspension systems are typically fixed to both the pivoting member, for example an equalizer beam or balancer, and the chassis bracket by, for example, force fitting or bonding the bushing between the two elements. Therefore, in use, the bushing will deflect angularly as the pivoting member pivots about the bracket. Minor angular deflections of up to 1°, such as those which occur when absorbing micro-shocks and vibrations, are handled effectively by the bushing. However, major angular deflections, such as those that occur when driving through potholes and the like, have been found to be a major cause of wear on conventional elastomeric bushings. Consequently an elastomeric bushing will tear and split, and may need to be replaced after as little as 50,000 km. This is in contrast with the remainder of the suspension system which could otherwise have an operational life of 250,000 km or more.
Another drawback of conventional pivot assemblies is that conventional elastomeric bushings are only able to deflect by at most 10°, and conventional pivot assemblies therefore typically provide mechanical stoppers which physically limit the rotation of the pivot member. However, it has been found that it would be advantageous to enable the pivot assembly to take angular displacements of up to 20° in situations such as braking and shock loading. Typically, when this limit is reached and the bushing is stopped from deflecting more than 10°, the equalizer assembly is prevented from further distributing the load between front and rear leaf springs, thereby reducing the overall effectiveness of tandem suspension and its load distribution capabilities.
Hence, in light of the afore-mentioned, there is a need to provide an improved pivot assembly for a tandem suspension which by virtue of its design and components would be able to overcome at least some of the prior art problems.